@H2O MAN,
Well, pollster.com is following many polls, not just doing one poll at a time. You can see the individual poll results as dots in the graph, though.
From these individual polls, the trend is calculated - the red and blue line in the graph. If several polls, over a longer time, show McCain with a lead, then that will be reflected in the graph. But if he just jumps ahead of Obama in three or four polls, for a couple of days, then the graph may change slightly, but never to the point where McCain would be ahead - simply because it doesn't necessarily reflect the actual trend. Simply because individual polls can be off.
Here's an explanation for the trend line from pollster.com:
Quote:Here is a way to think about this: suppose the last 5 polls in a race are 25, 27, 29, 31 and 33. Which is a better estimate of where the race stands today? 29 (the mean) or 33 (the local trend)? Since support has risen by 2 points in each successive poll, our estimator will say the trend is currently 33%, not the 29% the polls averaged over the past 2 or 3 weeks during which the last 5 polls were taken. Of course real data are more noisy than my example, so we have to fit the trend in a more complicated way than the example, but the logic is the same. Our trend estimates are local regression predictions, not simple averaging. If the data have been flat for a while, the trend and the mean will be quite close to each other. But if the polls are moving consistently either up or down, the trend estimate will be a better estimate of opinion as of today while the simple average will be an estimate of where the race was some 3 polls ago (for a 5 poll average-- longer ago as more polls are included in the average.)
And for more information on numbers and polls, just go ahead and ask nimh....